Validating an integrated workload scale for vessel traffic services: a comparative assessment with NASA-TLX

Crestelo Moreno, Fernando; García Maza, Jesus A. · 2026 · Crossref

DOI: 10.1007/s12144-025-08918-1

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Summary

This study addresses the critical need for real-time workload assessment tools in Vessel Traffic Services (VTS), a safety-critical domain where operator fatigue and cognitive overload significantly increase the risk of human error. Existing instruments, such as the NASA Task Load Index (NASA-TLX), rely on retrospective self-reporting and lack validation for VTS Operators (VTSOs). To fill this gap, the authors developed and validated the Integrated Workload Scale (IWS), a color-coded, real-time tool co-designed with VTSOs to categorize cognitive demands based on task type, urgency, and complexity. The primary research question was whether the IWS demonstrates acceptable psychometric properties, specifically reliability and construct validity, for use in operational maritime settings. The study employed a mixed-methods design involving 23 VTSOs (14 males, 9 females; mean age 42) from two Maritime Rescue Coordination Centers in Spain. Data collection included continuous thermographic monitoring using an FLIR E60 camera to detect physiological markers of fatigue, specifically nasal apex temperature changes. Participants also completed standardized self-report questionnaires, including the NASA-TLX, Borg Rating of Perceived Exertion (RPE), Stanford Sleepiness Scale, and Epworth Sleepiness Scale, administered before and after shifts. The IWS categorized tasks into five levels: Level 1 (routine monitoring), Level 2 (standard coordination), Level 3 (visitor handling), Level 4 (merchant traffic control), and Level 5 (emergency response). Workload was calculated as a time-weighted average of these levels during shifts. Statistical analyses included correlational assessments to evaluate convergent validity and paired t-tests to analyze changes in perceived exertion. The results demonstrated that the IWS possesses strong internal consistency and high convergent validity, showing a significant correlation with NASA-TLX scores (ρ = 0.842, p < .001). The average NASA-TLX workload rating was 27.14, indicating moderate perceived task demand. IWS scores correlated positively with task complexity and emergency activity, supporting its construct validity. Thermographic data revealed that nasal temperatures stabilized around 32 °C during night shifts, compared to broader fluctuations during day shifts, indicating heightened physiological fatigue. Additionally, Borg RPE scores increased significantly with time on duty (ρ = 0.459, p = .008), with 72% of operators reporting higher fatigue during night shifts. The study also noted that pre-task rest is a key variable in counteracting fatigue. The significance of these findings lies in establishing the IWS as a reliable, context-sensitive instrument for real-time workload monitoring. Unlike retrospective measures, the IWS enables immediate operational decision-making and dynamic staffing adjustments. The study highlights that fatigue in VTS is not solely a function of traffic volume but is heavily influenced by shift work, circadian disruption, and task complexity. By validating a tool that integrates cognitive workload with physiological indicators, the research provides actionable insights for improving fatigue risk management systems, enhancing operator well-being, and reducing safety incidents in maritime traffic services.

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Summary generated by qwen3.6-27b-nvidia on 2026-08-10; verification: verified.

Topics

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• workload measurement
• mental demand

Information type

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• Empirical Findings: self report data, physiological data
• Methodological Resource: metric or index